1. Technical Field.
This invention relates generally to carrier tapes of the kind used to transport components from a component manufacturer to a different manufacturer that assembles the components into new products. More specifically, this invention relates to carrier tapes for storing electronic surface mount components and for supplying those components seriatim to a machine. The invention further relates to a method for manufacturing such carrier tapes.
2. Description of the Related Art.
In general, carrier tapes that are used to transport components from a component manufacturer to a different manufacturer that assembles the components into new products are well known. For example, in the field of electronic circuit assembly, electronic components are often transferred from a source of such components to a specific location on a circuit board for attachment thereto. The components may be of several different types, including surface mount components. Particular examples include memory chips, integrated circuit chips, resistors, connectors, dual in-line processors, capacitors, gate arrays, etc. Such components are typically affixed to a circuit board that may later be incorporated into an electronic device.
Rather than manually affixing each individual electronic component to a circuit board, the electronics industry makes extensive use of robotic (i.e., automated) placement machines, sometimes known as "pick-and-place" machines, which grasp a component at a specific location (the source) and place it at another specific location (the circuit board). To ensure the sustained operation of the robotic placement machine, a continuous supply of electronic components must be furnished to the machine at a predetermined rate and location to permit the machine to be programmed to repeat a precise sequence of movements during every cycle. It is therefore important that each such component be located in the same position (i.e. the point at which the robotic placement machine grasps the component) as each preceding and succeeding component.
One way to provide a continuous supply of electronic components to a desired location is to use a carrier tape. Conventional carrier tapes generally comprise an elongated strip that has a series of identical pockets formed at predetermined, uniformly spaced intervals along the length of the tape. Each pocket is shaped to closely receive an electronic component. The tapes also normally include a series of through holes uniformly spaced along one or both edges of the elongated strip. The through holes, frequently referred to as advancement holes, drive holes, sprocket holes or indexing holes, receive the teeth of a drive sprocket that advances the tape toward the robotic placement machine.
Typically, the carrier tapes are manufactured in one location, wound onto a reel, and transported to a second location where the tape is unwound and continuously fed to a machine that automatically loads the pockets with electronic components. The advancement holes accurately position the pockets with respect to the component loading machine to help ensure that each component is deposited into a pocket and in the proper orientation for subsequent removal by the robotic placement machine. A continuous cover tape may then be applied over the elongated strip to retain the components in the pockets.
Usually, the loaded carrier tape is then wound onto another reel for transport to the manufacturing location where the new products are being assembled. The loaded carrier tape is then unwound from the reel and fed to the robotic placement machine that removes the components from the pockets and places them onto the circuit board. The advancement holes accurately position the loaded carrier tape with respect to the robotic placement machine to ensure precision removal of the stored components.
Carrier tapes are often manufactured in a thermoforming operation in which a web of thermoplastic polymer is delivered to a mold that forms the component pockets. The thermoformed web is usually cooled to ambient temperature before being delivered to another manufacturing station where the advancement holes are punched through the web by an automated punching machine. While these operations can be run at an acceptably high line speed, they also require precision handling of the web to ensure that the subsequently punched advancement holes are properly aligned and registered with respect to the component pockets. Failure to provide adequate alignment and registration can result in improper subsequent positioning of the carrier tape in the component loading machine and/or in the robotic placement machine. Since the component pockets are formed separately from the advancement holes, it is necessary to regain registration when the thermoformed web is delivered to the punching machine. This is not always easy to do.
In another manufacturing approach, the thermoplastic polymer web is indexed to a machine that both thermoforms the pockets and punches the advancement holes. Carrier tape segments of about 15 centimeters are often formed in each cycle, and the registration between the component pockets and the advancement holes in any given segment is typically quite good. However, carrier tapes of up to about 1000 meters in length are often provided on a single reel. This requires about 6000 combined thermoforming/punching operations to produce a single reel of carrier tape, and it can be difficult to maintain consistent component pocket-to-advancement hole registration over these distances. In addition, this process is associated with the use of a flat forming die which can limit the speed of the manufacturing line.
Both of the processes described above involve punching a thermoformed web to provide the advancement holes. Punching creates waste (slugs) and dust that may contaminate the components, which can be of special concern when manufacturing precision electronic parts. In addition, the thermoplastic web may be a tough, resilient material that can be difficult to punch. As a result, the punches wear out or break and have to be frequently replaced. Precision punches are expensive and replacing them is a time consuming process that requires delicate realignment and retiming of the new punch.
Consequently, there is a continuing need for component carrier tapes that display excellent advancement hole-to-component pocket registration, especially over the long distances typically found on reel-wound carrier tapes used in the electronics industry. There is also a need for a manufacturing process that provides a means for advancing the carrier tape without punching holes, especially if this can be done without generating slugs or dust.